The quick answer to your question is no,
molecules do not stop moving at absolute zero.
They move much less than at higher temperatures,
but they still have small vibrations at absolute
zero. Sometimes classical definitions of
absolute zero say that it is the temperature
where all molecular motion ceases, but that
definition is not technically correct.
Because molecules are very small, their
movement is governed by the laws of quantum
mechanics. Sometimes that means that they behave
in ways that seem to be peculiar and
unpredictable, because we are used to observing
classical (large scale) physics in our daily
When molecules move, they move in very
specific ways. One type of molecular movement is
vibration. The vibrations of the atoms and bonds
are restricted because of the way quantum
mechanics relates to their symmetry. Different
types of vibrations have different energy
levels. At higher temperatures, different modes
of vibration (more vibrations) are available to
the molecule. As molecules are cooled, they are
able to vibrate in fewer and fewer ways, so
movement slows approaching absolute zero.
However, quantum mechanics has a strange feature
called zero point energy. That means that even
at its lowest energy state, a molecule does not
have zero energy. Molecules, even at absolute
zero, always have energy. The vibrational zero-
point energy of the molecule still corresponds
to movement, so even though the molecule is at
absolute zero, it is still moving.
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